The dynamics of montmorillonite clay dispersion and morphology development in immiscible ethylene–propylene rubber/polypropylene blends

Influence of Polymer Processing on the Double Electrical Percolation Threshold in PLA/PCL/GNP Nanocomposites

For the first time, the double electrical percolation threshold was obtained in polylactide (PLA)/polycaprolactone (PCL)/graphene nanoplatelet (GNP) composite systems, prepared by compression moulding and fused filament fabrication (FFF). Using scanning electron microscopy (SEM) and atomic force microscopy (AFM), the localisation of the GNP, as well as the morphology of PLA and PCL phases, were evaluated and correlated with the electrical conductivity results estimated by the four-point probe method electrical measurements. The solvent extraction method was used to confirm and quantify the co-continuity in these samples. At 10 wt.% of the GNP, compression-moulded samples possessed a wide co-continuity range, varying from PLA55/PCL45 to PLA70/PCL30. The best electrical conductivity results were found for compression-moulded and 3D-printed PLA65/PCL35/GNP that have the fully co-continuous structure, based on the experimental and theoretical findings. This composite owns the highest storage modulus and complex viscosity at low angular frequency range, according to the melt shear rheology. Moreover, it exhibited the highest char formation and polymers degrees of crystallinity after the thermal investigation by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. The effect of the GNP content, compression moulding time, and multiple twin-screw extrusion blending steps on the co-continuity were also evaluated. The results showed that increasing the GNP content decreased the continuity of the polymer phases. Therefore, this work concluded that polymer processing methods impact the electrical percolation threshold and that the 3D printing of polymer composites entails higher electrical resistance as compared to compression moulding.

Improved electrical conductivity of TPU/carbon black composites by addition of COPA and selective localization of carbon black at the interface of sea-island structured polymer blends

The electrical percolation threshold of carbon black (CB) in thermoplastic polyurethane (TPU) decreases by 46% with the incorporation of 20 wt% polyamide copolymer (COPA) through selective localization of CB particles at the interface of sea-island structured TPU/COPA blends. Composites with a composition of TPU/20 wt% COPA/9 wt% CB were prepared by four different mixing sequences and their morphologies were investigated by FESEM and TEM. The majority of CB particles were observed at the interface of sea-island structured blends irrespective of the compounding sequence used, although the percentage of CB particles at the interface is considerably less in the composite prepared by adding COPA to premixed TPU/CB. The driving force for the interfacial localization of most CB particles is the hydrogen bonding of CB with both TPU and COPA, which is confirmed by FTIR and DMA investigations. CB particles act like Janus particle-type compatibilizers with bonded TPU molecules toward the TPU phase and bonded COPA chains toward the COPA phase. Highly efficient conductive paths are formed through the CB-covered domains and a short inter-domain distance.

Effect of carbon nanotubes on morphology evolution of polypropylene/polystyrene blends: understanding molecular interactions and carbon nanotube migration mechanisms

MWCNT migration among domains in conjunction with viscosity and elastic effects are important factors governing the morphological changes in the PP:PS blend nanocomposites.

Using water to modify the localization of clay in immiscible polymer blends

The injection of water during melt blending modified the localization of clay in immiscible polymer blends from one phase to the other and improved their dispersion state.

Morphology development of PP/POE blends with high loading of magnesium hydroxide

A co-continuous structure of PP/POE was maintained even after a large amount of Mg(OH)₂ was added, which was the key factor for tolerating high loading of additives and retaining acceptable tensile properties.

Morphology Control and Stabilization in Immiscible Polypropylene and Polyamide 6 Blends with Organoclay

In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.

The Effect of Feeding Method and Compatibilizer on Nanoclay Partitioning and Microfibrillar Morphology Development in PP/PBT/Organoclay Blend Nanocomposite Fibers

The role of feeding method, as an important parameter in competition with thermodynamic parameters, on determining the nanoclay partitioning and its impact on microfibril formation in PP/PBT blend nanocomposite fibers were investigated. In the direct feeding method in which all components were fed into the extruder simultaneously, the major part of nanoclay with almost unchanged interlayer d-spacing was located in the PP matrix and the rest of the nanoclay partitioned into the PBT dispersed phase. However in the PBT based masterbatch method nanoclay, due to much greater melt intercalation occurred, remained in PBT droplets in the form of tactoids and/or platelets. In the masterbatch feeding method, incorporation of compatibilizer assisted more fraction tactiods and/or platelets to be transferred from PBT to the PP matrix while in the direct method it enhanced the extent of melt intercalation in the PP matrix. It was demonstrated that the nanoclay concentration in PBT droplets plays an important role in the extent of the microfibril formation during the melt spinning process. While at low organoclay loading (1 wt%) fine microfibrils could be formed in the fibers prepared by both methods of feeding, at higher organoclay loading (3,5 wt%) uniform microfibrils could hardly be developed in the fibers, particularly, in the masterbatch feeding method due to high melt elasticity of the PBT droplets and uneven distribution of platelets and/or tactoids in the droplets.

Clay platelet partition within polymer blend nanocomposite films by EFTEM

Transmission electron microscopy (TEM) is the main technique used to investigate the spatial distribution of clay platelets in polymer nanocomposites, but it has not often been successfully used in polymer blend nanocomposites because the high contrast between polymer phases impairs the observation of clay platelets. This work shows that electron spectral imaging in energy-filtered TEM (EFTEM) in the low-energy-loss spectral crossover region allows the observation of platelets on a clear background. Separate polymer domains are discerned by imaging at different energy losses, above and below the crossover energy, revealing the material morphology. Three blends (natural rubber [NR]/poly(styrene-butyl acrylate) [P(S-BA)], P(S-BA)/poly(vinyl chloride) [PVC], and NR/starch) were studied in this work, showing low contrast between the polymer phases in the 40-60 eV range. In the NR/P(S-BA) and P(S-BA)/PVC blend nanocomposites, the clay platelets accumulate in the P(S-BA) phase, while in the P(S-BA)/PVC nanocomposites, clay is also found at the interfaces. In the NR/starch blend, clay concentrates at the interface, but it also penetrates the two polymer phases. These observations reveal that nanostructured soft materials can display complex morphochemical patterns that are discerned thanks to the ability of EFTEM to produce many contrast patterns for the same sample.